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Teleporting larger objects becomes real possibility

6 February 2002

By Anil Ananthaswamy

The dream of teleporting atoms and molecules – and maybe even larger objects – has become a real possibility for the first time. The advance is thanks to physicists who have suggested a method that in theory could be used to “entangle” absolutely any kind of particle.

Quantum entanglement is the bizarre property that allows two particles to behave as one, no matter how far apart they are. If you measure the state of one particle, you instantly determine the state of the other. This could one day allow us to teleport objects by transferring their properties instantly from one place to another.

Until now, physicists have only been able to entangle photons, electrons and atoms, using different methods in each case. For instance, atoms are entangled by forcing them to interact inside an optical trap, while photons are made to interact with a crystal.

“These schemes are very specific,” says Sougato Bose of the University of Oxford. But Bose and Dipankar Home, of the Bose Institute in Calcutta, have now demonstrated a single mechanism that could be used to entangle any particles, even atoms or large molecules.

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Beam splitter

To see how it works, consider the angular momentum or “spin” of an electron. To entangle the spins of two electrons, you first need to make sure they’re identical in all respects but their spin. Then you shoot the electrons simultaneously into a beam splitter.

This device “splits” each electron into a quantum state called a superposition, which gives it an equal probability of travelling down either of two paths. Only when you try to detect the electron do you know which path it took. If you split two electrons simultaneously, both paths could have one electron each (which will happen half of the time) or either path could have both.

Bose and Home show mathematically that whenever one electron is detected in each path, they will be entangled. While a similar effect has been demonstrated before for photons, the photons used were already entangled in another way, even before they reached the beam splitter.

“One of the advances we have made is that these two particles could be from completely independent sources,” says Bose.

Massive particles

The technique should work for any objects – atoms, molecules and who knows what else – as long as you can split the beam into a quantum superposition.

Anton Zeilinger, a quantum physicist at the University of Vienna in Austria, has already shown that this quantum state is possible with buckyballs – football-shaped molecules of C60. Although entangling such large objects is beyond our technical abilities at the moment, this is the first technique that might one day make it possible.

Any scheme that expands the range of particles that can be entangled is important, says Zeilinger. Entangling massive particles would mean they could then be used for quantum cryptography, computing and even teleportation.

“It would be fascinating,” he says. “The possibility that you can teleport not just quantum states of photons, but also of more massive particles, that in itself is an interesting goal.”